THE MATHEMATICAL MODELING OF THERMOCHEMICAL PROCESS OF A TWO-STAGE DOWNDRAFT GASIFICATION

ABSTRACT

This work developed a mathematical model to predict the temperature profile in the pyrolysis zone, and the feedstock feed rate of the KU-KPS two-stage downdraft gasification process using wood chips as feedstock. The obtained temperature profile is an important input parameter to calculate the gas composition of volatile gas in the pyrolysis zone of the gasification process. The feedstock feed rate is also useful to evaluate the gas generation rate, thermal efficiency, and gas composition in producer gas of gasification. Thermochemical concepts were applied to derive the energy and mass balance equations composed of chemical, kinetic, and three modes of heat transfer; conduction, convection, and radiation. The feedstock was treated as a porous medium. The equations were solved by the implicit finite difference method on the node of 200 and conversion criteria of 10−6. Experiments were also conducted to validate the model results. The validation results showed that the maximum temperature deviation between model and experiment was 62° C at the combustion temperature of 790° C while for the feedstock feed rate it had a deviation of 0.94 kg/h at the rate of 14.7 kg/h. The experimental uncertainty was also analyzed based on a 95% level of confidence. The total experimental uncertainties of temperature and feedstock feed rate were 72° C and 0.95 kg/h, respectively.